For example, since resin molding materials having high transparency such as polycarbonate resin or acrylic resin have superior light weight, impact resistance, processability, integration ability with surrounding components and design properties in comparison with inorganic glass, they are widely used in place of organic glass in various types of applications in order to take advantage of these merits.
However, since these resins are inferior to inorganic glass in terms of surface abrasion resistance and hardness, there are many cases in which they are used in the form of polymer substrates provided with a hard coating layer in which a polymer substrate is laminated with a hard coating layer for preventing damage to the polymer substrate.
In the case of polymer substrates having a hard coating layer used in automobile window materials in particular (typically referred to as resin glazing materials), a level of abrasion resistance comparable to that of inorganic glass is required to ensure mechanical strength required for use as a window material as well as visibility in terms of driving safety, while environmental performance is required so as to withstand outdoor exposure for long periods of time. With respect to environmental performance, it is necessary for these polymer substrates to demonstrate performance capable of passing various types of tests in anticipation of direct contact with moisture including inclement weather, use under both high humidity and dry conditions, use under both high temperature and low temperature conditions and exposure to high levels of ultraviolet rays. The previously proposed products can be said to be inadequate for use as resin glazing materials capable of stably realizing all of these required performance levels.
With respect to the abrasion resistance of inorganic glass and the like, when referring to standards such as the FMVSS205 safety standard applied in the U.S. or the ECE R43 safety standard applied in Europe, the required level of abrasion resistance with respect to windows used at sites requiring visibility during driving is defined as an increase in haze value (ΔH) of less than 2% or 2% or less as determined with a Taber abrasion test carried out for 1000 revolutions as defined in ASTM D1044.
Although polymer substrates having a hard coating layer (see, for example, Patent Documents 1, 2 and 3), obtained by depositing an organic silicon-based oxide polymer on a resin substrate by plasma-enhanced chemical vapor deposition (PE-CVD) using an organic silicon compound (such as organosiloxane, organosilane or silazane) for the raw material, have been proposed for use as resin glazing materials for applications requiring both high abrasion resistance and outdoor weather resistance in this manner, typically in the case of providing a hard coating layer having high hardness formed by PE-CVD on an outermost surface, due to the generation of considerable interface stress between the high hardness hard coating layer and the underlayer on which that layer is laminated, it becomes difficult to ensure durability and reliability of the resulting hard coating layer. There are also many cases in which resistance to a boiling water test, which is an accelerated test relating to direct contact with moisture in the usage environment and long-term standing in high-humidity, high-temperature environment (to be referred to as boiling water resistance), as well as resistance to a high-temperature endurance test, which is an accelerated test relating to temperature change in an usage environment (to be referred to as heat resistance), are inadequate, frequently resulting in the observation of defective adhesion of the high hardness hard coating layer as well as other defects such as peeling phenomena or crack formation.
For example, the aforementioned Patent Document 1 proposes a plastic laminate obtained by sequentially laminating an acrylic resin heat-cured film, an organosiloxane-based resin heat-cured film, and PE-CVD film using an organic silicon compound as raw material on at least one side of a plastic substrate, wherein the PE-CVD film is composed of a gradient zone, in which the abundance ratio of oxygen atoms to silicon atoms (O/Si ratio) increases gradually from the interface with the heat-cured film of the aforementioned organosiloxane-based resin, and a subsequent flat zone, in which the aforementioned ratio is nearly constant, and Examples 1 and 2 therein disclose laminates that realize Taber abrasion resistance performance of 2.0% or less, which is an object of that invention, boiling water resistance as determined by a boiling water immersion test of 2 hours, and heat resistance of 1000 hours at 110° C.
Although these exemplified references were carried out by the present applicants, with respect to the method used to evaluate boiling water resistance, several problems were determined to occur during the course of examinations conducted by the present applicants after the exemplified patent documents were filed. Namely, although the duration of immersion in boiling water is indicated as being 2 hours, it was determined that making the duration of immersion in boiling water to be at least 3 hours and preferably 4 hours or more is preferable in terms of adequately ensuring long-term reliability such as water resistance or moisture resistance. In addition, with respect to the method used to evaluate an adhesion test after immersing in boiling water, it was determined that simply evaluating immediately after testing using the crosscut tape test is inadequate, and that it is necessary to evaluate and confirm results at least 7 days after carrying out the test. This is because it was determined that, since there are many cases in which internal stress (and frequently compressive force) generated during layer formation remains in the silicon oxide layer formed by PE-CVD, and due to the action thereof, there are cases observed in which layer separation occurs over time.
On the basis of these findings, it was decided to carry out evaluation of adhesion in the boiling water test of the present invention according to the procedure described below.
Namely, an adhesion test is carried out in accordance with a crosscut tape test in compliance with JIS K5400 after immersing a polymer substrate having a hard coating layer in boiling water at 100° C., removing the polymer substrate from the boiling water after retaining in the boiling water for 3 hours, removing any adhered moisture, and finally allowing to stand in a room temperature environment for 2 hours. The crosscut tape test is carried out by forming 10×10 squares cut out at 1 mm intervals with a cutter knife in the form of a grid followed by affixing and adhering tape having a prescribed adhesive force (such as Nichiban Cellophane Tape™) and then peeling off the tape. The result for adhesion immediately after carrying out the crosscut tape test (state in which the layer is peeled or separated from the surface) was designated as the “initial result”, while the result obtained after the passage of 7 days after carrying out the crosscut tape test was designated as the “elapsed result”, and adhesive performance and the reliability thereof were judged to be favorable only in the case not only the “initial result”, but also the “elapsed result” were favorable.
According to this evaluation method, when boiling water resistance of the laminate of the aforementioned Patent Document 1 was reevaluated, although the “initial result” was favorable (100/100), according to the “elapsed result”, separation of the PE-CVD layer laminated according to the PE-CVD method occurred at sites where crosscuts were made. Namely, the result of evaluation in the case of Example 1 was 70/100 (layer separation occurred in 30 of the 100 squares), and the result of evaluation in the case of Example 2 was 0/100 (layer separation occurred in all 100 squares), with satisfactory results being unable to be obtained for both examples, thereby resulting in a need to improve performance.
In addition, in the aforementioned Patent Document 2, a laminate is proposed that has a plurality of coating layers comprising an outermost layer (I), obtained by plasma polymerization of an organic silicon compound, a lower layer (II), having a silicone coating composition containing a composite oxide fine particle dispersion, a silicone resin, a curing catalyst and a solvent, and a lower layer (III) consisting of an arbitrary acrylic resin, on an organic resin substrate, and in Examples 2, 4, 5 and 7, laminates are disclosed that have Taber abrasion resistance performance of 2.0% or less, which is an object of that invention. In addition, a correlation between individual properties of each layer that composes the laminates and performance is also disclosed.
However, in these examples, the haze values of the laminates are high at 2.7% to 3.0%, thereby resulting in the problem of images transmitted through the laminates being unclear, and since this makes their use in applications requiring visibility difficult, an object of present applicants in the form of a polymer substrate having a hard coating layer is not realized. Moreover, in these examples, although results for water resistance performance (using test conditions consisting of 3 days at 65° C.) and an accelerated weather resistance test are disclosed, there is no disclosure of boiling water resistance performance or heat resistance performance, and thus the object of the present applications in the form of a polymer substrate having a hard coating layer and a high level of weather resistance performance cannot be said to be realized.
In addition, in the aforementioned Patent Document 3, a multilayer product is proposed that is composed of a base material, a first layer obtained with a partial condensate of organosiloxane, and a second layer containing plasma-polymerized organic silicon and deposited at a power level of 106 J/Kg to 106 J/Kg in the presence of excess oxygen, results are disclosed in Example 2 indicating favorable appearance after an outdoor exposure test conducted for 1 year in Florida, U.S.A. (absence of microcracks) and favorable adhesion, and results indicating favorable appearance after an accelerated xenon weather resistance test at a cumulative radiation level of 6875 KJ/m2 (absence of microcracks) and favorable adhesion are disclosed in Examples 4 and 5.
However, in these examples, although the results of an accelerated weather resistance test are disclosed, there is no disclosure of boiling water resistance performance or heat resistance performance, and an object of the present applicants in the form of a polymer substrate having a hard coating layer and a high level of weather resistance performance cannot be said to be realized.